Publications

Issue Archive

A Three-Frequency Feed for Millimeter-Wave Radiometry

Monday, 01 October 2012

This wave feed operates at frequencies approximately
five times higher than current feeds and provides
greater bandwidth.

A three-frequency millimeter-wave
feed horn was developed as part of an
advanced component technology task
that provides components necessary for
higher-frequency radiometers to meet
the needs of the Surface Water and
Ocean Topography (SWOT) mission.
The primary objectives of SWOT are to
characterize ocean sub-mesoscale processes on 10-km and larger scales in the
global oceans, and to measure the global
water storage in inland surface water
bodies, including rivers, lakes, reservoirs,
and wetlands.

In this innovation, the feed provides
three separate output ports in the 87-to-
97-GHz, 125-to-135-GHz, and 161-to-
183-GHz bands; WR10 for the 90-GHz
channel, WR8 for the 130-GHz channel,
and WR5 for the 170-GHz channel.
These ports are in turn connected to
individual radiometer channels that will
also demonstrate component technology
including new PIN-diode switches
and noise diodes for internal calibration
integrated into each radiometer
front end. For this application, a prime
focus feed is required with an edge
taper of approximately 20 dB at an illumination
angle of ±40°. A single polarization
is provided in each band.
Preliminary requirements called for a
return loss of better than 15 dB, which
is achieved across all three bands. Good
pattern symmetry is also obtained
throughout all three-frequency bands. This three-frequency broadband millimeter-
wave feed also minimizes mass
and provides a common focal point for
all three millimeter-wave bands.

In order to achieve similar E and H
plane beam widths over the combined
87-to-183-GHz band ring, loaded slots
are employed in the corrugated portion
of the feed. The feed operates in a flareangle
limited condition, which gives
approximately constant beam width
across the entire band, and provides a
common phase center located near its
apex. The half-flare angle for the feed is
approximately 30°. Analysis and optimization
of the overall feed design
employed a combination of finite element
and mode-matching tools.

The illumination requirements and
relative frequency spacing for this application
are similar to those required for
the Scanning Multichannel Microwave
Radiometer (SMMR) on Seasat, the
(TOPEX)/Poseidon, and the Jason missions.
However, in this particular application
the required fractional bandwidth
is larger. Thus, while the three-frequency
feed horn described here shares
many features in common with the feed
previously developed for the above missions,
enhancements are necessary in
order to achieve broad band performance
and manufacturability in the millimeter-
wave bands.

This work was done by Daniel J. Hoppe,
Behrouz Khayatian, John B. Sosnowski, Alan
K. Johnson, and Peter J. Bruneau of Caltech
for NASA’s Jet Propulsion Laboratory. For more
information, contact This email address is being protected from spambots. You need JavaScript enabled to view it..
NPO-48528

Question of the Week

This week's Question: Last week, Elon Musk, chief executive of Tesla, said that the electric car maker would introduce autonomous technology, an autopilot mode, by this summer; the technology will allow drivers to have their vehicles take control...